<?php
$cfg = [
    0      => 'cfg-1',
    1      => 'cfg-1',
    'name' => 'hlq',
    'age'  => 18,
    'job'  => 'engineer',
];

$default = [
    0       => 'default-0',
    1       => 'default-1',
    'name'  => 'hlq',
    'age'   => 16,
    'hobby' => 'readding',
];

print_r($cfg + $default);
/**
 * (
 * [0] => cfg-1
 * [1] => cfg-1
 * [name] => hlq
 * [age] => 18
 * [job] => engineer
 * [hobby] => readding
 * )
 */

print_r(array_merge($cfg, $default));
/**
 * Array
 * (
 * [0] => cfg-1
 * [1] => cfg-1
 * [name] => hlq
 * [age] => 16
 * [job] => engineer
 * [2] => default-0
 * [3] => default-1
 * [hobby] => readding
 * )
 */